U.S. patent application number 09/973065 was filed with the patent office on 2002-04-25 for bearing device for driving wheel.
Invention is credited to Ogura, Hiroyuki, Takubo, Takayasu, Torii, Akira.
Application Number | 20020049091 09/973065 |
Document ID | / |
Family ID | 26601797 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020049091 |
Kind Code |
A1 |
Ogura, Hiroyuki ; et
al. |
April 25, 2002 |
Bearing device for driving wheel
Abstract
A bearing device for a driving wheel is provided to improve
service life thereof by preventing strain from being generated
inside the bearing device, where the strain is caused by
deformation of a hub ring and an inner ring by loads acting in a
direction of forming a contact angle. In the bearing device for a
driving wheel comprising an outer ring on an inner peripheral
surface of which raceways of double rows are formed, a hub ring on
an outer peripheral surface of which one of the raceways opposing
the raceways of the outer ring and a wheel mounting flange are
formed, an inner ring fitted onto a small-diameter stepped portion
of the hub ring and formed with the other raceway on its outer
peripheral surface, rolling elements of double rows installed
between each of the raceways between the outer ring and the hub
ring and between the outer ring and the inner ring, and a constant
velocity universal joint having the joint outer ring of which a
shaft portion is fitted into the hub ring through serrated portions
in such a manner that torque is transmittable, a pilot portion is
provided between a base part of the shaft portion of the joint
outer ring and the small-diameter stepped portion of the hub ring,
and the clearance of the pilot portion is set to 0.4 mm or
less.
Inventors: |
Ogura, Hiroyuki;
(Shizuoka-ken, JP) ; Torii, Akira; (Shizuoka-ken,
JP) ; Takubo, Takayasu; (Shizuoka-ken, JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN
1050 CONNECTICUT AVENUE, N.W.
SUITE 600
WASHINGTON
DC
20036
US
|
Family ID: |
26601797 |
Appl. No.: |
09/973065 |
Filed: |
October 10, 2001 |
Current U.S.
Class: |
464/139 |
Current CPC
Class: |
F16C 19/386 20130101;
F16C 43/04 20130101; F16D 2003/22326 20130101; F16C 19/186
20130101; F16C 2240/46 20130101; F16C 2326/02 20130101; F16D 3/223
20130101; F16D 3/16 20130101; Y10S 464/906 20130101 |
Class at
Publication: |
464/139 |
International
Class: |
F16D 003/16 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2000 |
JP |
2000-309538 |
Oct 10, 2000 |
JP |
2000-309543 |
Claims
What is claimed is:
1. A bearing device for a driving wheel comprising: an outer member
on an inner peripheral surface of which raceways in double rows are
formed; an inner member on an outer peripheral surface of which
raceways opposing to raceways of the outer member and a wheel
mounting flange are formed; rolling elements of double rows
provided between each of the raceways of the outer member and the
inner member; and a constant velocity universal joint having a
joint outer ring of which a shaft portion is inserted into the
inner member in such a manner that torque is transmittable, the
bearing device rotatably supporting a wheel on a automobile body,
wherein a pilot portion is provided between a base part of the
shaft portion of the joint outer ring and an end portion of the
inner member.
2. The bearing device according to claim 1, wherein a clearance of
the pilot portion is 0.4 mm or less.
3. The bearing device according to claim 1 or 2, wherein the outer
member integrally has raceways of double rows and a wheel mounting
flange on its inner and outer peripheral surfaces,
respectively.
4. The bearing device according to claim 1 or 2, wherein the inner
member comprises a hub ring on an outer peripheral surface of which
the wheel mounting flange, one of the raceways, and a
small-diameter stepped portion are formed, and a inner ring, which
is a separate member, fitted onto the small-diameter stepped
portion and formed with the other raceway on its outer peripheral
surface.
5. The bearing device according to claim 1 or 2, wherein the pilot
portion is positioned on a line extending from the line of forming
a contact angle for the rolling elements on the raceway of the
inner member.
6. The bearing device according to claim 1 or 2, wherein serrated
portions, formed on the inner member and the shaft portion of the
joint outer ring in such a manner that torque is transmittable, are
fitted together with an interference.
7. The bearing device according to claim 1 or 2, wherein a surface
hardened layer is formed in an area extending from a base portion
of the wheel-mounting flange to an end portion of the inner
ring.
8. The bearing device according to claim 1 or 2, wherein the inner
member has a swaged portion in which an end portion of the inner
member is plastically deformed toward its outside-diameter side,
and the swaged portion is butted against a shoulder portion of the
joint outer ring in a linear contact.
9. The bearing device according to claim 8, wherein the inner
member and the shaft portion of the joint outer ring are detachably
fixed together in an axial direction by a fastening element.
10. The bearing device according to claim 1 or 2, wherein the
rolling elements are tapered rollers.
11. The bearing device according to claim 10, wherein the inner
member comprises a hub ring on an outer peripheral surface of which
the wheel mounting flange, one of the raceways, and a
small-diameter stepped portion are formed, and a inner ring, which
is a separate member, fitted onto the small-diameter stepped
portion and formed with the other raceway on its outer peripheral
surface, and another pilot portion is formed between the end
portion of the inner ring butted against the shoulder portion of
the joint outer ring and the base part of the shaft portion of the
joint outer ring.
12. The bearing device according to claim 11, wherein from among
the two pilot portions formed between the base part of the shaft
portion of the joint outer ring and the hub ring, and between the
base part of the shaft portion of the joint outer ring and the end
portion of the inner ring, a clearance of the pilot portion formed
between the base part of the shaft portion of the joint outer ring
and the end portion of inner ring is set smaller than that formed
between the base part of the shaft portion of the joint outer ring
and the hub ring.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a bearing device for a
driving wheel for rotatably supporting a driving wheel of an
automobile on an automobile body.
[0003] 2. Description of the Related Art
[0004] Different types of bearing devices for driving wheels of
automobiles have been proposed depending on use. For example, a
bearing device shown in FIG. 4 has as major structural elements a
hub ring 1, an inner ring 2, rolling elements 3 and 4 of double
rows, an outer ring 5, and a constant velocity universal joint
6.
[0005] The hub ring 1 is formed with an outboard raceway 7 on its
outer peripheral surface and provided with a wheel-mounting flange
9 for mounting a wheel. Hub bolts 10 for fixing a wheel disk are
provided on the wheel-mounting flange 9 at equal intervals in a
circumferential direction. The inner ring 2 is fitted onto a
small-diameter stepped portion 11 formed on an outer peripheral
surface of an inboard-side end portion of the hub ring 1, and an
inboard raceway 8 is formed on an outer peripheral surface of the
inner ring 2.
[0006] The inner ring 2 is pressed into position with an
appropriate interference in order to prevent its creeping. Raceways
of double rows are constituted by the outboard raceway 7 formed on
the outer peripheral surface of the hub ring 1 and by the inboard
raceway 8 formed on the outer peripheral surface of the inner ring
2. The inner ring 2 is pressed onto the small-diameter stepped
portion 11 of the hub ring 1, and a joint outer ring 21 is inserted
into the hub ring 1 from its inboard side in an axial direction.
Then, the joint outer ring 21 is fastened with the hub ring 1. With
this process, an end portion of the inner ring 2 is butted against
a shoulder portion 28 of the joint outer ring 21, so that the inner
ring 2 is prevented from loosening and preload to a bearing portion
15 is controlled.
[0007] On an inner peripheral surface of the outer ring 5, raceways
12 and 13 of double rows are formed, which oppose to the raceways 7
and 8 of the hub ring 1 and the inner ring 2, and the outer ring 5
is provided with an automobile-body-mounting flange 14 for mounting
a bearing device on an automobile body. The flange 14 is fixed with
bolts to a knuckle extending from a suspension device of the
automobile body.
[0008] The bearing portion 15 is of a double-row angular ball
bearing structure in which the rolling elements 3 and 4 are
provided between a group of the raceways 7 and 8 formed on outer
peripheral surfaces of the hub ring 1 and the inner ring 2 and a
group of raceways 12 and 13 formed on an inner peripheral surface
of the outer ring 5, and the rolling elements 3 and 4 in each row
are supported by cages 16 and 17 at equal intervals in a
circumferential direction.
[0009] At opening portions of both ends of the bearing portion 15,
a pair of seals 18 and 19 sealing an annular space formed by the
outer ring 5, the hub ring 1 and the inner ring 2 is fitted into an
inside of the hole at an end portion of the outer ring 5 so as to
prevent leakage of grease filled inside and ingress of water or
foreign matters from outside.
[0010] The constant velocity universal joint 6 comprises the joint
outer ring 21 provided at one end of the shaft 39 and formed with
the track groove 20 on its inner peripheral surface, a joint inner
ring 41 on an outer peripheral surface of which a track groove 40
opposing to the track groove 20 of the joint outer ring 21 is
formed, balls 42 installed between the track groove 20 of the joint
outer ring 21 and the track groove 40 of the joint inner ring 41,
and a cage 43 provided between the joint outer ring 21 and the
joint inner ring 41 for supporting the balls 42.
[0011] The joint outer ring 21 has a mouth portion 22 accommodating
the joint inner ring 41, the balls 42 and the cage 43, and a shaft
portion 23 extending in an axial direction from the mouth portion
22 and being formed with a serrated portion 24 on its outer
peripheral surface. The shaft portion 23 is inserted into a
through-hole of the hub ring 1 so that they are fitted together
through serrated portions 24 and 25 formed on the outer peripheral
surface of the shaft portion 23 and an inner peripheral surface of
the through-hole, respectively. Then, the constant velocity
universal joint 6 is fixed to the hub ring 1 by tightening a nut 27
on an external thread portion 26 formed on an end of the shaft
portion 23. Preload of the bearing portion 15 is controlled by
axial force applied by tightening the nut 27.
[0012] In the bearing device in FIG. 4, preload of the bearing
portion 15 is controlled by tightening torque of the nut 27, while
in the bearing device shown in FIG. 5 in which a swaging process is
employed in assembling it, preload control by fastening torque of
the nut 27 is not required.
[0013] In this bearing device, a projection end portion of the
small-diameter stepped portion 11 of the hub ring 1 is swaged by
plastically deforming it toward an outside-diameter side, and the
hub ring 1 and the inner ring 2 are unitized together by the swaged
portion, or a swaged portion 31, by which the inner ring 2 is
prevented from loosening and preload of the bearing portion 15 is
controlled. Therefore, when engaging a bolt 33 into a threaded hole
32 formed on the shaft portion 23 of the joint outer ring 21 after
inserting the shaft portion 23 through the though-hole of the hub
ring 1, the joint outer ring 21 is fixed to the hub ring 1 with
tightening torque that is necessary and sufficient to prevent the
joint outer ring 21 from loosening.
[0014] On the other hand, in a bearing device using balls as the
rolling elements 3 and 4, because the contact angle is set to about
35.degree., loads acting on the inner ring 2 in a direction of
forming a contact angle are also taken at the swaged portion 31 of
the hub ring 1 butted against the shoulder portion 28 of the joint
outer ring 21. Here, the term "contact angle" means the angle
measured between the lines of action of force transmitted to the
rolling elements 3 and 4 by the raceways 7 and 8, and a plane (or a
radial plane) perpendicular to the axis of a bearing.
[0015] Accordingly, the small-diameter stepped portion 11 of the
hub ring 1 and the raceway 8 of the inner ring 2 tend to be
deformed by loads acting in a direction of forming a contact angle.
With increasing amount of deformation of the small-diameter stepped
portion 11 of the hub ring 1, the possibility of breakage of the
hub ring 1 and fretting between the hub ring 1 and the inner ring 2
increases. Further, an increased amount of deformation of the
raceway 8 of the inner ring 2 tends to cause deterioration of
rolling service life, rise in temperature on the raceway 8, and
loss in axial force (or preload) caused by fretting between the
inner ring 2 and the shoulder portion 28 of the joint outer ring
21. When the small-diameter stepped portion 11 of the hub ring 1
and the raceway 8 of the inner ring 2 become to tend to undergo
deformation as described above, strain produced inside the bearing
may cause deterioration of service life of the bearing device.
SUMMARY OF THE INVENTION
[0016] An object of the invention is to improve the service life of
a bearing device by preventing strain from being generated inside
the bearing device, in which the strain is caused by deformation of
a hub ring and an inner ring by loads acting in a direction of
forming a contact angle.
[0017] A bearing device for a driving wheel of the invention
includes an outer member on an inner peripheral surface of which
raceways of double rows are formed, an inner member on an outer
peripheral surface of which raceways opposing to the raceways of
the outer member and a wheel mounting flange are formed, rolling
elements of double rows installed between each of the raceways of
the outer member and the inner member, and a constant velocity
universal joint having a joint outer ring of which a shaft portion
is fitted into the inner member in a manner that torque is
transmittable. The bearing device rotatably supports a wheel on an
automobile body. In this construction, a pilot portion is provided
between a base part of the shaft portion of the joint outer ring
and an end portion of the inner member. A clearance of the pilot
portion is preferably 0.4 mm or less.
[0018] By providing the pilot portion between the base part of the
joint outer ring and the inner member as described above, loads
acting in a direction of forming a contact angle prevents
deformation of the end portion of the inner member, so that
breakage of the inner member is prevented and fretting of the inner
member is reduced. Thus, service life of a bearing device is
improved, allowing providing a highly reliable bearing device
having long service life.
[0019] The invention is applicable to a bearing device having an
outer member integrally provided with raceways of double rows on
its inner peripheral surface and a wheel mounting flange on its
outer peripheral surface. Further, the invention is also applicable
to a bearing device having an inner member comprising a hub ring on
an outer peripheral surface of which a wheel mounting flange, one
of the raceways, and a small-diameter stepped portion are formed,
and an inner ring, which is a separate member, fitted to the
small-diameter stepped portion and on an outer peripheral surface
of which the other raceway is formed.
[0020] In the structure described above, the pilot portion is
positioned on a line extending from the line of forming a contact
angle for the rolling elements on the raceway of the inner member.
When the pilot portion is provided, loads acting in a direction of
forming a contact angle securely prevents deformation of the end
portion of the inner member, thereby facilitating further
improvement of service life of the bearing device.
[0021] In the structure described above, serrated portions formed
on both the inner member and the shaft portion of the joint outer
ring in such a manner that torque is transmittable are preferably
fitted together with an interference. By doing so, the inner member
and the shaft portion of the joint outer ring can be fitted
together without play.
[0022] It is also preferable that a surface hardened layer is
formed in an area extending from a base portion of the
wheel-mounting flange to an end portion of the inner member. By
doing so, rolling fatigue life is increased and fretting can be
reduced by increased surface hardness of an area including the
raceway of the inner member.
[0023] The present invention is characterized in that the inner
member has a swaged portion in which an end portion of the inner
member is plastically deformed toward its outside-diameter side,
and the swaged portion is butted against a shoulder portion of the
joint outer ring in a linear contact. By making the swaged portion
of the inner member and the shoulder portion of the joint outer
ring butt against each other in linear contact, noise from between
the swaged portion of the inner member and the shoulder portion of
the joint outer ring can be prevented from occurring.
[0024] The bearing device according to the invention is further
characterized in that the inner member and the shaft portion of the
joint outer ring are detachably fixed together in an axial
direction by a fastening element. In other words, fastening the
inner member and the shaft portion of the joint outer ring may be
made with fastening torque of a magnitude that is necessary and
sufficient for preventing the joint outer ring loosening from the
inner member. Therefore, besides a bolt or a nut, a fastening
member such as a clip and a snap ring may also be used for the
fastening.
[0025] The invention is also applicable for a bearing device using
tapered rollers as rolling elements and suitable for automobiles
that are inherently heavy.
[0026] In the structure having an inner member comprising a hub
ring on an outer peripheral surface of which a wheel mounting
flange, one of the raceways, and a small-diameter stepped portion
are formed, and an inner ring, which is a separate member, fitted
to the small-diameter stepped portion and on an outer peripheral
surface of which the other raceway is formed, another pilot portion
is formed between the end portion of the inner ring butted against
the shoulder portion of the joint outer ring and the base part of
the shaft portion of the joint outer ring. By forming the pilot
portion between the end portion of the inner ring and the base part
of the shaft portion of the joint outer ring, deformation of the
raceway of the inner ring is prevented by loads acting in a
direction of forming a contact angle, so that service life of the
bearing device can be improved.
[0027] In this case, from among the two pilot portions formed
between the base part of the shaft portion of the joint outer ring
and the hub ring, and between the base part of the shaft portion of
the joint outer ring and the end portion of the inner ring,
clearance of the latter pilot portion is preferably made smaller
than that of the former pilot portion.
[0028] The nature, principle, and utility of the invention will
become more apparent from the following detailed description when
read in conjunction with the accompanying drawings in which like
parts are designated by like reference numerals or characters.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] In the accompanying drawings:
[0030] FIG. 1 is a cross sectional view of an embodiment of the
invention, showing an example of a structure of a bearing device
for a driving wheel using balls as rolling elements;
[0031] FIG. 2 is a cross sectional view of another embodiment of
the invention, showing an example of a structure of a bearing
device for a driving wheel using tapered rollers as rolling
elements;
[0032] FIG. 3 shows a modified example of the bearing device in
FIG. 2, showing a cross sectional view of a bearing device for a
driving wheel provided with two pilot portions;
[0033] FIG. 4 shows an example of a conventional bearing device for
a driving wheel, showing an example of a structure in which a joint
outer ring is fixed to a hub ring with a nut; and
[0034] FIG. 5 shows another example of a conventional bearing
device for a driving wheel, showing an example of a structure in
which a hub ring and an inner ring are unitized by swaging.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] An embodiment shown in FIG. 1 shows a bearing device for a
driving wheel in which a swaging process is applied in assembling
the bearing device and balls are used as rolling elements. The
bearing device comprises as main structural elements, for example,
a hub ring 1 and an inner ring 2 as inner members, rolling elements
3 and 4 in double rows, an outer ring 5 as an outer member, and a
constant velocity universal joint 6.
[0036] The hub ring 1 has an outboard raceway 7 and a
wheel-mounting flange 9 for mounting a wheel on its outer
peripheral surface. Hub bolts 10 for fixing a wheel disk are
provided on the wheel-mounting flange 9 at equal intervals in a
circumferential direction. The inner ring 2 is fitted onto a
small-diameter stepped portion 11 formed on an outer peripheral
surface of an inboard end portion of the hub ring 1, and an inboard
raceway 8 is formed on an outer peripheral surface of the inner
ring 2.
[0037] The inner ring 2 is pressed into position with an
appropriate interference in order to prevent creeping. The outboard
raceway 7 formed on the outer peripheral surface of the hub ring 1
and the inboard raceway 8 formed on the outer peripheral surface of
the inner ring 2 constitute double raceways. A projection end
portion of the small-diameter stepped portion 11 of the hub ring 1
is plastically deformed to be swaged outward, and the swaged
portion, or a swaged portion 31, serves to prevent the inner ring 2
from loosening and to control preload of a bearing portion 15.
[0038] An outer ring 5 has double row raceways 12 and 13 opposing
to the raceways 7 and 8 of the hub ring 1 and the inner ring 2
formed on an inner peripheral surface of the outer ring 5, and is
provided with an automobile-body mounting flange 14 for mounting
the bearing device on a automobile body. The automobile-body
mounting flange 14 is fixed with bolts to a knuckle(not shown)
extending from the suspension device of the automobile body.
[0039] The bearing portion 15 is of a double-row angular ball
bearing structure in which the rolling elements 3 and 4 are
provided between a group of the raceways 7 and 8 formed on the
outer peripheral surfaces of the hub ring 1 and the inner ring 2
and a group of the raceways 12 and 13 formed on an inner peripheral
surface of the outer ring 5, and the rolling elements 3 and 4 in
each row of the raceways are supported by cages 16 and 17 at equal
intervals in a circumferential direction.
[0040] At opening portions of both ends of the bearing portion 15,
a pair of seals 18 and 19 for sealing an annular space formed by
the outer ring 5, the hub ring 1, and the inner ring 2 are fitted
into an inside of the hole at an end portion of the outer ring 5 in
order to prevent leakage of grease filled inside and ingress of
water or foreign matter from outside.
[0041] The constant velocity universal joint 6 comprises a joint
outer ring 21 provided at one end of a shaft 39 and having a track
groove 20 formed on its inner peripheral surface, a joint inner
ring 41 on outer peripheral surface of which a track groove 40
opposing to the track groove 20 of the joint outer ring 21 is
formed, balls 42 installed between the track groove 20 of the joint
outer ring 21 and the track groove 40 of the joint inner ring 41,
and a cage 43 provided between the joint outer ring 21 and the
joint inner ring 41 for supporting the balls 42.
[0042] The joint outer ring 21 has a mouth portion 22 accommodating
the joint inner ring 41, the balls 42, and the cage 43, and a shaft
portion 23 extending in an axial direction from the mouth portion
22 and being formed with a serrated portion 24 on its outer
peripheral surface. The shaft portion 23 is inserted through a
through-hole of the hub ring 1, and the through-hole of the hub
ring 1 and the shaft portion 23 are fitted together by serrated
portions 24 and 25 formed respectively on an outside of the shaft
portion 23 and an inner peripheral surface of the through-hole.
Then, the constant velocity universal joint 6 is fixed to the hub
ring 1 by fastening a nut 27 on an external thread portion 26
formed on an end of the shaft portion 23. The portions called
serrated portions 24 and 25 also include spline besides
serration.
[0043] In the bearing device according to the embodiment, a
projection end portion of the small-diameter stepped portion 11 of
the hub ring 1 is swaged to unitize the hub ring 1 and the inner
ring 2 together to control preload of the bearing portion 15 by the
swaged portion 31 of the hub ring 1. Therefore, the joint outer
ring 21 may be fixed to the hub ring 1 with the nut 27 with
tightening torque that is necessary and sufficient to prevent the
shaft portion 23 of the joint outer ring 21 loosening from the hub
ring 1. Besides a nut or a bolt, a fastening member (not shown)
such as a clip and a snap ring may be used to detachably fix the
shaft portion 23 of the joint outer ring 21 to the hub ring 1.
[0044] Because the embodiment of the bearing device for a driving
wheel using balls as rolling elements 3 and 4 has a contact angle
of about 35.degree., loads acting on the inner ring 2 in a
direction of forming a contact angle are taken by the swaged
portion 31 of the hub ring 1 butted against the shoulder portion 28
of the joint outer ring 21. Therefore, in this embodiment, a pilot
portion 35 is provided between a base part 34 of the shaft portion
of the joint outer ring 21 and the small-diameter stepped portion
11 of the hub ring 1. The pilot portion 35 is positioned on a line
extending from the line of forming a contact angle for the rolling
elements 4 on the inboard raceway 8 of the inner ring 2, so that
the axes of the hub ring 1 and the shaft portion 23 are aligned to
secure their coaxiality.
[0045] The pilot portion 35 is formed by expanding an outside
diameter of the base portion 34 of the shaft portion of the joint
outer ring 21, and at the same time, expanding the inner diameter
of the small-diameter stepped portion 11 of the hub ring 1 to a
diameter larger than that of the serrated portion 25. The pilot
portion 35 is thus formed and a clearance dimension `a` at the
pilot portion is set to 0.4 mm or less. Providing the clearance `a`
of the pilot portion makes it easier to insert the shaft portion 23
into the through-hole of the hub ring 1 when installing the
constant velocity universal joint 6 in position. The clearance `a`
of the pilot portion means a half of the difference between the
inner diameter of the small-diameter stepped portion 11 of the hub
ring 1 and the outer diameter of the base part 34 of the shaft
portion of the joint outer ring 21.
[0046] By providing the pilot portion 35 as described above,
deformation of the small-diameter stepped portion 11 of the hub
ring 1 is prevented by loads acting in a direction of forming a
contact angle, and as a result, breakage of the hub ring 1 is
prevented, and occurrence of fretting between the hub ring 1 and
the inner ring 2 is reduced. Further, loads in a direction of
forming a contact angle prevent deformation of the raceway 8 of the
inner ring 2, improving rolling life and preventing rise in
temperature. Also, loss in axial force (or preload) is prevented by
decreased occurrence of fretting between the inner ring 2 and the
shoulder portion 28 of the joint outer ring 21. Thus, service life
of a bearing device is improved. When the clearance `a` at the
pilot portion is greater than 0.4 mm, desired effect of preventing
deformation of the small-diameter stepped portion 11 of the hub
ring 1 and that of the raceway 8 of the inner ring 2 can not be
obtained.
[0047] Further, by making the swaged portion 31 of the hub ring 1
and the shoulder portion 28 of the joint outer ring 21 butt against
each other in linear contact, noise from between the swaged portion
31 of the hub ring 1 and the shoulder portion 28 of the joint outer
ring 21 is prevented from occurring. The serrated portions 24 and
25 formed on an outer peripheral surface of the shaft portion 23 of
the joint outer ring 21 and on the inner peripheral surface of the
hub ring 1 are fitted together with an interference given by, for
example, a helix angle prepared on the serrated portion 24.
[0048] Further, a surface-hardened layer 36 is formed in an area
(excluding an area of the swaged portion 31) extending from a base
portion of the wheel mounting flange 9 to the small-diameter
stepped portion 11 of the hub ring 1. The base part of the wheel
mounting flange 9 is an outer peripheral surface, or a sealing
surface portion, of the hub ring 1 with which a seal lip of a seal
18 installed at an outboard end portion of the outer ring 5
slidingly contact. The surface hardened layer 36 is formed in an
area (excluding the area of the swaged portion 31) extending from
the sealing surface portion via the raceway 7 to the small-diameter
stepped portion 11.
[0049] From among each portion of the surface-hardened layer 36,
the sealing surface portion is slidingly contacted with the seal
lip of the seal 18, so that the sealing surface portion requires
wear resistance. The raceway 7 requires durability because the
rolling elements 3 roll thereon, and the small-diameter stepped
portion 11 requires creep resistance and fretting resistance,
because it fits into the inner ring 2. The swaged portion 31 does
not require the surface-hardened layer 36 to be formed thereon,
because the portion requires ductility.
[0050] Induction hardening is suited for a heat treatment to form
the surface-hardened layer 36. By effectively using advantages of
induction heating, an induction hardening process as a surface
hardening process enables to freely select portions at which the
surface-hardened layer 36 is formed, providing wear resistance and
improving fatigue strength. Induction hardening is a method of
producing heat by directly converting electrical energy to heat
energy within metal using an electromagnetic induction phenomenon,
and an induction heat treatment using this method has many
features. Specifically, an induction heat treatment enables local
heating, allows to freely select the depth of a hardened layer, and
enables to control so as not to give remarkable thermal effect to
portions other than the area to be hardened, so that
characteristics of a base metal is maintained unaffected.
Therefore, the swaged portion 31 may be left as a untreated base
metal, with the desired surface-hardened layer 36 being allowed to
be formed in an area extending from the sealing surface portion via
the raceway 7 to the small-diameter stepped portion 11.
[0051] Rotation-life tests were carried out for a bearing device of
the first embodiment in FIG. 1 for different clearance of the pilot
portion, for example, and results that are described below were
obtained. Results of the service life tests presenting operation
hours of 255 hours and a temperature rise of 50.degree. C. or less
were obtained with a structure in which the clearance `a` of the
pilot portion of 0.4 mm is provided between the small-diameter
stepped portion 11 of the hub ring 1 and the base part 34 of the
shaft portion of the joint outer ring 21.
[0052] Contrary to this, in a structure without providing the pilot
portion 35, only results of the service life tests presenting
operation hours of 83 hours and a temperature rise of from 60 to
80.degree. C. were obtained.
[0053] The test results described above show that the operation
hours of the former structural example is three times or more as
long as those of the latter structural example, and that
temperature increase is also prevented. Therefore, it is obvious
that it is easier to improve service life of a bearing device with
the former structural example.
[0054] An embodiment shown in FIG. 1 is a bearing device employing
a swaging process in assembling the bearing device and using balls
as the rolling elements 3 and 4. FIG. 2 shows a bearing device as
another embodiment suited for, for example, automobiles that are
inherently heavy. In this embodiment, tapered rollers are used as
the rolling elements 3 and 4, and preload of the bearing portion 15
are controlled by tightening torque applied by the nut 27.
[0055] The bearing device (see FIG. 1) using balls as the rolling
elements 3 and 4 has a contact angle of about 35.degree., so that
loads acting on the inner ring 2 in a direction of forming a
contact angle act toward a face on which the shoulder portion 28 of
the joint outer ring 21 and the inner ring 2 butt against each
other. Contrary to this, in the bearing device (see FIG. 2) using
tapered rollers as the rolling elements 3 and 4, a contact angle is
generally set to a smaller value of 16.degree. to 20.degree. to
obtain a higher load capacity, so that loads in a direction of
forming a contact angle act toward the small-diameter stepped
portion 11 of the hub ring 1 and the base part 34 of the shaft
portion of the joint outer ring 21. Therefore, in this embodiment,
a pilot portion 35 is provided between the base part 34 of the
shaft portion of the joint outer ring 21 and the small-diameter
stepped portion 11 of the hub ring 1. The clearance `a` of the
pilot portion is set to 0.4 mm or less in the same manner as the
embodiment in FIG. 1.
[0056] Further, FIG. 3 shows still another embodiment of the
invention. In the bearing device of this embodiment, the pilot
portion 35 described above is formed between the base part 34 of
the shaft portion of the joint outer ring 21 and the small-diameter
stepped portion 11 of the hub ring 1, and at the same time, a pilot
portion 37 is also provided between an end portion of the inner
ring 2 butted against the shoulder portion 28 of the joint outer
ring 21 and the base part 34 of the shaft portion of the joint
outer ring 21. The latter pilot portion, or the pilot portion 37,
is formed by enlarging the diameter of the base part 34 of the
shaft portion of the joint outer ring 21 so that the base part 34
is extended to the area of clearance between the end face of the
small-diameter stepped portion 11 of the hub ring 1 and the
shoulder portion 28 of the joint outer ring 21.
[0057] By forming the pilot portion 37, as described above, between
the end portion of the inner ring 2 and the base part of the shaft
portion of the joint outer ring 21, deformation of the raceway 8 of
the inner ring 2 can be prevented by loads acting in a direction of
forming a contact angle. Accordingly, rolling life and temperature
rise are improved and rise in temperature and loss of axial force
(or preload) are prevented because of reduced occurrence of
fretting between the inner ring 2 and the shoulder portion 28 of
the joint outer ring 21, so that service life of the bearing device
is improved.
[0058] From among the two pilot portions 35 and 37 formed
respectively between the base part 34 of the shaft portion of the
joint outer ring 21 and the hub ring 1, and between the base part
34 of the shaft portion of the joint outer ring 21 and the end
portion of the inner ring 2, clearance `b` of the pilot portion
formed between the base part 34 and the inner ring 2 is set smaller
than the clearance `a` of the pilot portion formed between the base
part 34 and the hub ring 1.
[0059] That is, the clearance `a` of the pilot portion formed
between the small-diameter stepped portion 11 of the hub ring 1 and
the base part 34 of the shaft portion of the joint outer ring 21 is
set to 0.4 mm or less as described above, while the clearance `b`
of the pilot portion formed between the base part 34 of the shaft
portion of the joint outer ring 21 and the end portion of the inner
ring 2 is set to 0.05 mm or less. If the clearance `b` is greater
than 0.05 mm, the desired effect of preventing deformation of the
raceway 8 of the inner ring 2 can not be obtained. From among the
two pilot portions of 35 and 37, one of the pilot portions, or the
pilot portion 37, prevents the inner ring 2 from deforming, and
when higher loads are applied, the other pilot portion, or the
pilot portion 35, prevents the hub ring 1 from deforming.
[0060] Further, in the same manner as the embodiment in FIG. 1, it
is so constituted that a surface-hardened layer 36 is formed in an
area extending from the base portion of the wheel mounting flange 9
to the small-diameter stepped portion 11 of the hub ring 1, and the
surface-hardened layer 36 ends in the vicinity of an end face of
the small-diameter stepped portion 11 of the hub ring 1.
[0061] Rotation-life tests were carried out for the bearing device
of the embodiment shown in FIG. 2, for different clearance
dimensions of the pilot portions, for example, and results
described below were obtained. Results of service life tests
presenting operation hours of 165 hours and a temperature rise of
50.degree. C. or less were obtained in a structure in which the
clearance `a` of the pilot portion of 0.4 mm was formed between the
small-diameter stepped portion 11 of the hub ring 1 and the base
part 34 of the shaft portion of the joint outer ring 21, and also
the clearance `b` of the pilot portion of 0.05 mm was formed
between the end portion of the inner ring 2 and the base part 34 of
the shaft portion of the joint outer ring 21.
[0062] Contrary to this, only results of service life tests
presenting operation hours of 52 hours and a temperature rise in a
range from 72.degree. C. to 90.degree. C. were obtained in a
structure in which clearance of the pilot portion of 2 mm was
formed between the small-diameter stepped portion 11 of the hub
ring 1 and the base part 34 of the shaft portion of the joint outer
ring 21, and at the same time, clearance of the pilot portion of
8.75 mm was formed between the end portion of the inner ring 2 and
the base part 34 of the shaft portion of the joint outer ring
21.
[0063] The test results described above show that the operation
hours of the former structural example is three times or more as
long as those of the latter structural example, and also a rise in
temperature is prevented in the same example. Therefore, it is
obvious that the former structural example facilitates improvement
of a bearing device.
[0064] While there has been described what are at present
considered to be preferred embodiments of the invention, it will be
understood that various modifications may be made thereto, and it
is intended that the appended claims cover all such modifications
as fall within the true spirit and scope of the invention.
* * * * *